A team of Boston University researchers has created a metamaterial — material specifically engineered and shaped to have certain properties — that can absorb noise while letting air flow through, creating the possibility of future silent fans, drones and other mechanical devices.
Normally, the way to eliminate noise is to build thick, heavy walls around the source of a sound. This works fine with stationary setups, such as power generators, but some things simply cannot work if walled off, drones being the most notable example, as they are both unpleasantly noisy and need a free flow of air to function.
However, the Boston University team has come up with a different idea — a polymer material that can be molded into various shapes. Thorough computer simulations would determine what exact shape it should be and at what exact place it should be installed in order to reflect most of the noise back towards its source.
In a video uploaded to the university's YouTube channel, a ring-shaped prototype is placed at the end of a plastic tube with a booming speaker inside. When the experimental muffler is removed, the sound suddenly becomes significantly louder, which is reflected in a corresponding graph. While this is only a prototype, it is the combination of silencing and allowing free flow of air that makes it revolutionary.
"Sound is made by very tiny disturbances in the air. So, our goal is to silence those tiny vibrations," the scientists say. "If we want the inside of a structure to be open air, then we have to keep in mind that this will be the pathway through which sound travels."
It is not immediately clear whether the ring-shaped muffler works on a single frequency or on a wide spectrum of frequencies. However, the scientists underscore that the muffler can be molded into various shapes, including cubes or hexagons, which could be used to build entire sound-removing walls that let air flow through.
"We can design the outer shape as a cube or hexagon, anything really," the researchers said. "When we want to create a wall, we will go to a hexagonal shape. The idea is that we can now mathematically design an object that can block the sounds of anything."
The scientists say they are now working on applying their invention to drones. While drones mostly fly overhead, the scientists believe that a ring-shaped muffler could be placed beneath a machine's rotors to cancel the noise that would otherwise spread downward.
"Drones are a very hot topic," the researchers say, adding that large companies like Amazon are interested in using drones to deliver goods, but "people are complaining about the potential noise."